Thermoforming of Composite Materials

The main function of packaging is the safety of the product against environmental influences in order to maintain the quality between production and consumption. Consumers notice this as the best-before date. Spoiled products receive great media attention, which, in turn, lead to significant economic consequences for the respective companies. As the result of this, product safety is a central point of quality management for all prepackaging companies.

In order to protect foodstuffs and pharmaceuticals, a sufficient barrier effect of the packaging has to be ensured. Apart from the tightness of seams and other challenging spots, this tightness is particularly related to the permeation properties of the material in use. Composite materials with a barrier layer made of a substance like ethylen-vinyl alcohol (EVOH) are used for more demanding products The permeability of the material is not only influenced by the packaging material itself, but also by the production process, as in the thermoforming of the molding, as well as the downstream processes, like, for example, the sterilization- and transport process. Thermoforming is a common procedure to produce cups, shells and blister pack for the food- and pharmaceutical industry. In order to maintain the necessary safety for the product, barrier materials are used for the greater part. During the optimization of the production- and packaging process different requirements have to be taken into consideration. As an example, decreasing the thickness of the packaging material in order to lower the cost of the packaging, leads to a reduction of the barrier effect and a resulting change in process stability, which may finally lead to a modification in web guidance. Process stability, however, is a vital factor for product safety. As the determination of the permeability may take several weeks, concurrent quality control is only used in exceptional cases. A significantly faster procedure is the determination of the wall thickness. This, however, is not fully transferable to permeability, as further parameters like material stretching, contribute to the result.

Pretests have shown that the stretching of the material, which results from the forming process, leads to a 2.5 % decrease in the barrier layer (as opposed to the original material thickness) and may even lead to damages of the barrier layer and, consequently, to insufficient protection. For this reason the question of which process parameters of the thermoforming process influence the barrier properties of composite materials is investigated within the course of this research project. The second aim is the reduction of stress on the material by uniform stretching which consequently shows the saving potential of the material whilst maintaining the barrier effect.